root, do an rpm reading with and without the fine mesh Bru-line filter. In my limited tests, the filter acts as a restrictor plate. I saw a drop in peak rpms with the filter installed. Your fuel mileage will go up because the engine will not rev out like before. As the filter only comes in one size (I think), this effect will be noticed on larger engines more than small ones. At least this is what I found. If I was going to use a Bru-line on an engine larger than .45, I'd think about using the coarse filter element.